The present invention generally relates to a winding machine and more particularly, to an overload avoiding arrangement for a winding machine such as a chain block, hand hoist or the like.
Generally, a winding machine is so constructed that a driven member and a brake biasing member coupled to each other through a friction member are fitted onto a driving shaft, thereby to transmit a rotational force applied to a manually rotated member to the driving shaft through said brake biasing member and said driven member. In the winding machine of the above described type, there has conventionally been proposed, for example, in U.S. Pat. No. 4,251,060 a winding machine provided with an overload avoiding arrangement which is so adapted that the rotation of the manually rotated member is not transmitted to the load side during overloading.
FIG. 1 shows the prior art as referred to above and so arranged that a retainer ring 3 is movably fitted onto a brake biasing member 2 for movement in the axial direction, while a friction transmission ring 5 is threaded onto said retainer ring 3, and onto an outer peripheral portion of the friction transmission ring 5, there is fitted a manually rotated member 6 having a frusto-conical inner surface 7 following a corresponding frusto-conical friction outer surface 4 of said friction transmission ring 5. On the other hand, the manually rotated member 6 is depressed so that its frusto-conical inner surface 7 closely contacts the frusto-conical friction outer surface 4 of the friction transmission ring 5, by belleville springs 9 fitted over an outer periphery of the retainer ring 3 and positioned by a spring support flange 8 of said retainer ring 3. Thus, it is so arranged that under the overloaded state of an object to be transferred, a rotational torque of the manually rotated member 6 necessary for the winding becomes larger than a frictional force produced by the belleville springs 9 between the manually rotated member 6 and the friction transmission ring 5, whereby the manually rotated member 6 is idly rotated to prevent the winding function.
However, in the known construction as described above, since the belleville springs 9 are held in direct contact with the spring support flange 8 at one end face of the manually rotated member 6, abrasion takes place on both of the belleville springs 9 and the spring support flange 8 at the end of the manually rotated member 6, with each idle rotation of said manually rotated member 6, thus resulting in deterioration of the apparatus.
By the abrasion of the belleville springs 9, the depressing force of said springs 9 is undesirably altered, and consequently, gives rise to such an inconvenience that the overload set value varies according to the frequency or the number of times for use of the winding machine.
Other disadvantages inherent in the above prior art arrangement are such that, since the manually rotated member 6 is only supported, at its one end face, by the belleville springs 9 in a state of linear contact, except that it is supported by the frusto-conical friction outer surface of the friction transmission ring 5, in the case, for example, where the manually rotated member 6 is constituted by a hand chain wheel as in a chain block, if the pulling operation of the hand chain is effected through deviation towards the side of the belleville springs 9, the contact between the hand chain wheel and the friction transmission ring 5 becomes loose, thus tending to result in such disadvantages that the hand chain wheel is idly rotated even with respect to a load smaller than a set overload value.